Transducer

ABSTRACT

AN ELECTROACOUSTICAL TRANSDUCER IS DISCLOSED WHICH INCORPORATES, A DICED PIEZOELECTRIC CRYSTAL BACKED BY A PHENOLIC DISC, A RESILIENT PRESSURE RELEASE BUTYL RUBBER CUP, AN ALUMINUM BLOCK, AND A METALLIC CUP THAT CONTAINS SAID CRYSTAL, DISC, RUBBER CUP, AND ALUMINUM BLOCK. ELECTRODES ARE CONNECTED TO ALL OF THE ACTIVE END FACES AND THE BASE OF SAID DICED PIEZOELECTRIC CRYSTAL, AND ELECTRICAL WIRE CONDUCTORS ARE CONNECTED TO EACH OF SAID FACE ELECTRODES AND SAID BASE ELECTRODE. A BUTYL RUBBER PIEZOELECTRIC CRYSTAL, AND A AND RADIALLY FROM SAID DICED PIEZOELECTRIC CRYSTAL, AND A LIQUID ACOUSTICAL LENS IS EFFECTIVELY ASSOCIATED THEREWITH. A MOUNTING PIPE AND FLANGE ARE EFFECTIVELY CONNECTED TO SAID LENS AND METALLIC CUP FOR THE MOUNTING THEREOF ON A UTILIZATION APPARATUS.

Feb. 27, 1973 R. L. COOK ET AL TRANSDUCER 2 Sheets-Sheet 1 Filed Dec.13, 1971 vmw JP NI BSNOdSEIH EAILV'IBH United States Patent O 3,718,898TRANSDUCER Rufus Lee Cook and Donald L. Folds, Panama City, Fla.,assignors to the United States of America as represented by theSecretary of the Navy Filed Dec. 13, 1971, Ser. No. 207,266 Int. Cl.H04b 13/00 US. Cl. 340 12 Claims ABSTRACT OF THE DISCLOSURE Anelectroacoustical transducer is disclosed which incorporates a dicedpiezoelectric crystal backed by a phenolic disc, a resilient pressurerelease Butyl rubber cup, an aluminum block, and a metallic cup thatcontains said crystal, disc, rubber cup, and aluminum block. Electrodesare connected to all of the active end faces and the base of said dicedpiezoelectric crystal, and electrical wire conductors are connected toeach of said face electrodes and said base electrode. A Butyl rubberbaflie extends around and radially from said diced piezoelectriccrystal, and a liquid acoustical lens is effectively associatedtherewith. A mounting pipe and flange are effectively connected to saidlens and metallic cup for the mounting thereof on a utilizationapparatus.

STATEMENT OF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

FIELD OF THE INVENTION The present invention relates, in general, toelectromechanical transducers, and, in particular, it is an underwaterelectroacoustical imaging transducer having multiple, substantiallyindependent, piezoelectric energy converters separated and configured insuch manner as to provide signals representing predetermined discreteacoustical pressures occurring within a sensed composite distribution ofacoustical pressures.

DESCRIPTION OF THE PRIOR ART Heretofore, numerous electroacousticaltransducers have been employed for converting electrical energy toacoustical energy and vice versa. For many practical purposes, they havebeen eminently satisfactory, but for some purposes they leave a greatdeal to be desired. In those instances where the image resolution ofacquired underwater targets is less than desired, it is often the resultof insuflicient mechanical decoupling occurring between adjacentoperative posts of a piezoelectric crystal that is diced to have amosaic configuration.

SUMMARY OF THE INVENTION The instant invention includes a dicedpiezoelectric crystal having operative posts which are spaced in suchmanner as to have a distance of M2 between the center longitudinal axesof adjacent ones thereof, where )t is the wave length of the optimumoperative design frequency of the entire transducer. Suitable pressurerelease material is employed as a backing for the diced ceramicpiezoelectric crystal. The entire periphery of the diced piezoelectriccrystal array is surrounded by a butyl bafiEle having pyramidal shapedwedges, in order to promote acoustic isolation thereof from thedirections substantially normal to the propagation and responsedirections thereof and, hence, thereby reduce internal reflectionstherein. In addition, the crystal array is disposed within a liquid lensin such manner that the liquid thereof floods the spaces between all ofthe crystal elements, thereby allowing each element or post to operatein a substantially independent manner without acoustic energy beingcoupled therebetween.

Of course, as is usual with electroacoustical transducers, thetransducer constituting the subject invention is reversiblethat is, itbroadcasts acoustical energy in response to electrical excitation andproduces electrical energy in response to acoustical energy excitation.

Due to the unique structural configuration of the invention, itovercomes many of the disadvantages of the prior art and, thus, in somerespects, constitutes an improvement thereover.

Therefore, it is an object of this invention to provide an improvedreversible electromechanical transducer.

Another object of this invention is to provide an improved reversibleelectroacoustical transducer.

Another object of this invention is to provide an improved acousticimaging sensor.

Still another object of this invention is to provide a transducer havingindependent multiple electroacoustical energy converters which arecapable of selectively taking discrete electrical samples of a compositeacoustic pressure distribution.

A further object of this invention is to provide an improved method andmeans for mapping a pressure dis tribution of the type that would bepresent at the image surface of an acoustic imaging element, such as alens.

Another object of this invention is to provide an improved method andmeans for effecting a two-dimensional spatial sampling of a givenpressure field, such as a given acoustic pressure distribution over apredetermined area.

A further object of this invention is to provide a matrix ofpiezoelectric crystal elements, each of which has frequency response andimpedance characteristics that are similar to those of the others.

A further object of this invention is to provide a matrix ofpiezoelectric crystal elements, each of which exhibits a free fieldvoltage response that is essentially similar to that of the others.

Other objects and many of the attendant advantages will be readilyappreciated as the subject invention becomes better understood byreference to the following detailed description, when considered inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration ofthe invention, partly in cross-section, and partly in elevational view;

FIG. 2 is a cross-sectional view of the unique energy converter assemblyof FIG. 1;

FIG. 3 is a front'elevational view of the energy converter assembly ofFIGS. 1 and 2;

FIG. 4 is a diagram of a centered, square-configured matrix ofpiezoelectric sensor elements which are illustrated as being numbered ina preferred operational sequence within the subject invention;

FIG. 5 is a graphical representation of the reception sensitivity versusfrequency of a typical piezoelectric electroacoustical energy converterelement of the type incorporated in the subject invention;

FIG. 6 is a graphical representation of the response directivity patterneffected by each of the electroacoustical energy converter elements ofthe energy converter assembly of FIGS. 1 and 2; and

FIG. 7 is a block diagram of a typical system which may incorporate thetransducer constituting this invention to an advantage.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, thetransducer constituting this invention is shown as having a sphericalliquid lens 11 that is connected by any conventional means (such ascementing 12) to one end of an extension pipe 13, the other end of whichis secured to a mounting flange 14 having bolt holes 15 extendingtherethrough. Said lens 11, pipe 13, and flange 14 may also be connectedto their respective elements in any suitable, conventional manner thatwill provide a fixed relationship therebetween.

The outer peripheral boundary of lens 11 is, in fact, effected by anacoustically clear shell 16 constructed, for example, of anacrylonitrile-butadiene-styrene, a polypropylene material, apolyethylene material, or the like. Preferably, the cthat is, thedensity times sound velocityof the shell material should be such thatits acoustical characteristics closely approximate that of sea water orthe ambient environmental medium thereof, in the event the subjecttransducer is used in some other medium.

An acoustical energy refracting fluid 17, such as Freon, fluorocarbon,fluorolube, or the like, is used to fill shell 16. Such fluid, ofcourse, is intended to refract sound waves that pass through it andshell 16, so that incoming acoustic energy will be focused within apredetermined focal area for a given distance. It should also beselected so that the Wavelength of sound therein is about /2 the valueof the wavelength of sound in sea water. An electroacoustical imagingsensor assembly 18 is mounted within shell 16 and fluid 17 in suchmanner that it is in direct contact with said fluid 17 and also locatedwithin the aforesaid focal area thereof. Consequently, incoming sonicenergy will tend to be focused thereon. Because imaging sensor assembly18 is of considerable importance in the invention, it will be discussedmore fully subsequently.

An electrical cable 9 containing a plurality of insulated electricalconductors is connected to sensor assembly 18 and extends out of pipe13. It is, of course, suitable for being connected to any appropriateutilization apparatus. Obviously, imaging sensor assembly 18 andelectrical cable 19 should be mounted in such manner as to preventliquid or fluid 17 from leaking from shell 16. Hence, the joiningsurface of sensor assembly 18 and shell 16 should be made fluid tight byany convenient conventional means.

FIG. 2 shows the structure comprising the aforementionedelectroacoustical imaging sensor assembly 18.

In this particular embodiment, a piezoelectric ceramic disc 19, made ofa lead zirconate-titanate composition or any other suitablepiezoelectric material, is serrated in 90 directions in such manner asto have a plurality of slots 20 and 21 (see FIG. 3 for better view) ofwidth to and depth 1, thereby effecting a multiplicity of square orrectangular piezoelectric crystal elements 22 having the longitudinalaxes of adjacent ones one-half wavelength (k/2) apart (based on thevelocity of sound in water) for the intended operational frequency and,in addition, having a common piezoelectric crystal base 23. A pluralityof metallic electrodes 24 are respectively attached to the active frontend faces of said piezoelectric crystal elements 22, and a singleelectrode 25 is attached to the back of base 23 in such manner as tocover the entire area thereof that is opposite the active end faces ofthe aforesaid rectangular piezoelectric crystal elements 22.

A thin phenolic sheet 26, say of the order of .002 inch thick, isattached to the back of said base electrode 25, as by an epoxy or otheradhesive 27. A cup shaped resilient pressure releasing material 28,preferably made of Butyl rubber, is disposed around and back of thediced piezoelectric element 19 and phenolic backing sheet 26 connectedthereto. The lip thereof is preferably flush with the active face of theperipheral ones of said rectangular piezoelectric crystal elements.

In abutment with the back surface of rubber cup 28 is an aluminumblock-like disc 29, and surrounding the assembly described so far, is analuminum metal cup 31, with the lip thereof likewise flush with the lipof rubber cup 28.

Through a plurality of inline holes 32 through 36 respectively locatedthrough crystal base 23, phenolic disc 26, backing butyl rubber cup 28,aluminum disc 29, and metallic cup 31, are a plurality of size #37enameled wires 38, the ends of which are respectively soldered toelectrodes 24. Likewise, a wire 39 is threaded through in-line holes 40through 42 located in phenolic disc 27, rubber cup 28, aluminum disc 29,and metallic cup 31, respectively.

Surrounding the periphery of metallic cup 31 is a ringlike metallicframe 43 having an open front end 44, a recess 45, and a closed rear end46, and disposed within the recess thereof is a resilient butyl rubberring-like baffie 47. At the end of butyl ring baflle 47 which isadjacent to the active front end faces piezoelectric elements 22, saidbaflie is configured to have a plurality of radially spaced pyramidalshaped wedges 48 that protrude in the forward direction. so as to extendbeyond said active front end faces at least an amount equal to the depthof the wedges. In this preferred embodiment, baffle Wedges 48 havepointed apexes at the forward ends thereof; however, it should beunderstood that other geometrical configurations may be employed, ifoperational circumstances so warrant. Obviously, it would be well withinthe purview of one skilled in the art having the benefit of theteachings presented herewith to properly size and shape wedges 48, aswell as baflie 47 and the aforesaid piezoelectric crystal elements 22,in order to optimize the subject invention for any intended operationalsignal frequencies or to have any other desired operationalcharacteristics.

By means of a plurality of brackets 51, a rear bus bar 53 is connectedto the rear surface of frame 43. Preferably, bolts 54 and 55 extendingthrough holes 56 and 57 in brackets 51 are screwed into threaded holes58 and 59 of frame 43 and bus bar 53, respectively. Any number of suchbrackets may, of course, be used; hence, only the particulars of onebracket, viz, bracket 51 are disclosed here, in order to simplify thiscase as much as possible.

A plurality of electrical terminals 61 are respectively connected towires 38 that, in turn, are connected to the forward electrodes 24 ofpiezoelectric elements 22. Said terminals 61 are, in turn, connected toa like number of electrical conductors incorporated in theaforementioned cable 9, illustrated in FIG. 1. Likewise, anotherelectrical terminal 62 is connected to the wire connected to rearelectrode 25. As may readily be seen, terminals 61 and 62 all extendthrough and are, thus, mounted on bus bar 53.

A support shaft 63 having a flange 64 which is, in turn, connected tometallic cup 31 by bolts 65 (or any other conventional connection means)and may be optionally used as a mounting means for the entire energyconverter imaging sensor assembly 18. If used, it may be connected asdesirable to the aforesaid pipe 13 of FIG. 1, or it may be connecteddirectly to any other suitable mounting means (not shown) warranted byoperational circumstances.

FIG. 3 depicts a front view of electroaconstical sensor assembly 18without frame 43 and baffle 47 being attached thereto. As may readily beseen, it is preferably circular in shape; but, it has been determinedthat, although the entire circular area may contain piezoelectriccrystal posts or elements 22, only a particular, centered squareconfiguration 71 thereof provides optimum independent action or acousticimage sensing by each element.

For convenience in understanding data to be presented subsequently, theindividual ones of piezoelectric energy converted posts 22 in the squareconfiguration are numbered in the diagram of FIG. 4. They are numberedconsecutively from 1 to 100 starting at the lower left hand corner andworking across the bottom row and then working up in rows.

With a configuration of sensor posts 22 as shown in FIG. 4, it has beendetermined that the free field sensitivity for each post issubstantially similar to that shown in FIG. 5 for frequencies between400 and 500 kilocycles per second.

In addition, due to the acoustic isolation of each post (as a result ofits configuration, spacing, and disposition within the liquid lens) ofthe square configuration of FIG. 4, it has been determined, for example,that post 46 has a receiving directivity pattern similar to that shownin FIG. 6, and that the directivity response patterns of the others aresubstantially similar thereto. Hence, with such response patternseffected by practically all of the piezoelectric posts, it may also beseen that to a considerable extent each thereof is acoustically isolatedfrom its neighbors and, therefore, the combination thereof effects highresponse image resolution while viewing any particular incomingacoustical signal, say, that which has been reflected from an acquiredunderwater target. For example, the coupling levels betweenpiezoelectric elements 45 and 46 and the coupling levels betweenpiezoelectric elements 55 and 56element pairs which ordinarily would besubject to the maximum coupling conditions due to their central locationin the piezoelectric element matrixhave been determined to be of theorder of 25 db or less, a very worthwhile achievement, indeed.

FIG. 7 illustrates a carrier vehicle 81 containing a typicalecho-search-ranging system that may incorporate the subject invention toan advantage. In this particular instance said carrier vehicle will beconsidered to be a ship and said echo-search-ranging system willherewith be defined as a sonar system adapted for locating andidentifying underwater targets. Accordingly, a transceiver 82,preferably of the sonar type, is connected to a transducer 83 of thetype constituting this invention which, in turn, is well suited toacquire and identify a target 84, as will now be discussed more fullybelow during the discussion of the mode of operation of the invention.

MODE OF OPERATION The operation of the invention will now be discussedbriefly in conjunction with all of the figures of the drawmg.

As previously suggested, the entire transducer of substantially the typepictured in FIG. 1 is ordinarily mounted on a marine or submarinevehicle 81 in such manner that it is physically directed toward an areawhere it is desired to search for various and sundry targets. Forexample, if it is assumed that vehicle 81 of FIG. 7 is a marine vehicle,such as a ship or the like, and target 84 is an object laying on the seafloor, the subject transducer 83 would probably be mounted on vehicle 81in such manner as to look forward and downward. Then the transmitterportion of transceiver 82 would electrically energize transducer 83,thereby causing it to broadcast an acoustical energy search signal 85through water 86. Upon acquiring target 84, an echo 87 of said searchsignal would be reflected therefrom back to transducer 83. Of course, ifso desired, a separate electroacoustical transducer could be used toinitially broadcast search signal 85, and it then may be mounted onvehicle 81, on some other vehicle, or on some other suitable mountingplatform disposed at any place that would facilitate the searching forknown or unknown targets with acoustical search signals.

In order to effect search signal transmission, electrical energy issupplied to terminals 61 and 62 of FIG. 2, which, in turn, conduct it isso as to be applied across face electrodes 24 and base electrode 25. Asa result of the inherent piezoelectric characteristics existing in dicedcrystal 19, said electrical energy is converted to acoustical energyproportional thereto which is then broadcast in a forward direction aspressure waves from the front faces of all of the crystal elements beingenergized at any given instant. Said pressure waves are ordinarilyrefracted by fluid 17 as they pass therethrough before the sonificationof the ambient medium.

The reception process of transducer 83, is just the opposite of thatmentioned above. Incoming waves of acoustic pressure energy arerefracted by fluid or liquid 17 in such manner as to be focused on theactive front faces of piezoelectric elements 22. Due to theincorporation of the various pressure release backing materials andbaflle 44 having wedges 48, said crystal elements 22 are are not subjectto stray or spurious inputs that might otherwise impinge thereon fromdirections other than that of the intended sight or forward direction.In other words, the unique construction of the sensor assembly depictedin FIG. 2 improves the eificiency and resolution of the subjectinvention to a considerable extent as a result of either eliminating orisolating unwanted image distorting noise signals.

When the acoustic target echo signals are received by transducer 83,there are any number of ways of processing the data emanating therefrom,as the result of each active piezoelectric crystal element thereofconverting that portion of said echo signal received thereby into anelectrical signal proportional thereto. Hence, transducer 83, in effect,produces, say, bit signals each of which, for most practical purposes,are substantially independent of the others, as a result of theirrespectively having response patterns like that shown in FIG. 6 and,thus, having a minimum of cross-coupling between adjacent one thereof,Accordingly, it may be said that discrete samples of target reflectedacoustical signals are selected by and within the subject transducer.Whether said discrete samples are scanned consecutively, say, fromelements 1 through 100, or Whether they are data processedsimultaneously depends upon the type of transceiver employed and thetype of readout incorporated therein. Obviously, it would be well withinthe purview of the artisan having the benefit of the teachings presentedherewith to design and/ or select whatever type of transceiver would beoptimum for any given operational circumstances.

As shown in FIG. 5, the free field sensitivity of each piezoelectricelement is suflicient between 400 and 500 kHz to provide good targetresolution, regardless of the ggta processing and readout employed insonar transceiver It would perhaps be noteworthy that the subjectinvention is primarily intended to be used in sonar systems fordetection of underwater targets; however, it should be understood thatit may also be used in or in conjunction with any other appropriateenvironmental medium for detection and determination of various andsundry parameters of objects and materials existing therein.

Obviously, other embodiments and modifications of the subject inventionwill readily come to the mind of one skilled in the art having thebenefit of the teachings presented in the foregoing description and thedrawings. It is, therefore, to be understood that this invention is notto be limited thereto and that said modifications and embodiments areintended to be included within the scope of the appended claims.

What is claimed is:

1. A transducer, comprising in combination:

a piezoelectric crystal disc having a mosaic configuration of slotsextending partially therethrough in such manner as to effect a pluralityof predetermined electroacoustical energy converter elements having alike plurality of forward active end faces and a common base at the backthereof;

a plurality of electrodes attached to said plurality ofelectroacoustical energy converter elements, respectively;

another electrode connected to the back of said common base;

a thin phenolic disc connected to the back of the base electrode side ofsaid piezoelectric crystal disc;

a resilient presure release cup disposed around said piezoelectriccrystal disc and the thin phenolic disc connected thereto in such manneras to be in contact with the periphery and back thereof, respectively;

a metallic disc connected to the back of said resilient pressure releasecup;

a metallic cup holding said piezoelectric crystal disc, said phenolicdisc, said resilient pressure release cup, and said metallic disc as aunitary means;

a plurality of insulated electrical conductors threaded through saidmetallic cup, said metallic disc, said resilient pressure release cup,said phenolic disc, the common base of said mosaiced piezoelectriccrystal disc, and connected to the forward active faces of saidplurality of predetermined electroacoustical energy converter elements,respectively; and

another insulated electrical conductor threaded through said metalliccup, said metallic disc, said resilient pressure release cup, and saidphenolic disc, and connected to the aforesaid another electrode.

2. The device of claim 1, wherein said piezoelectric crystal disc ismade of lead zirconate and the mosaicing slots extending therethroughare disposed at such angles, respectively, as to cause the forwardactive faces of said plurality of predetermined electroacoustical energyconverter elements to have substantially square geometricalconfigurations.

3. The device of claim 1, wherein said thin phenolic disc has athickness of .002 inch.

4. The device of claim 1, wherein said resilient pressure release cupdisposed around said piezoelectric crystal disc and the thin phenolicdisc connected thereto in such manner as to be in contact with theperiphery and back thereof, respectively, is constructed of Butylrubber.

5. The device of claim 1, wherein said metallic disc connected to theback of said resilient pressure release cup is constructed of aluminum.

6. The invention of claim 1, further comprising:

a hollow shell of acoustically clear material elfectively connected tosaid transducer in such manner that said unitary means is located in thehollow thereof and said electrical conductors extend in fluid tightarrangement through the wall thereof; and

a predetermined acoustic energy refracting fluid filling the hollow ofsaid shell in such manner as to be in constant contact with the activeexternal surfaces of said plurality of predetermined electroacousticalenergy converter elements, including the slots therebetween and theforward active end faces thereof.

7. The invention of claim 6, further comprising means etfectivelyconnected to said hollow shell and the transducer disposed therein forthe mounting thereof on a predetermined carrier vehicle, so as to have apredetermined attitude relationship therewith.

8. The invention of claim 1, further comprising a baffle surrounding theperiphery of said metallic cup in such manner as to extend apredetermined radial distance therefrom.

9. The device of claim 8, wherein said baffle is constructed of rubberand includes a predetermined plurality of radially spaced, pyramidalshaped wedges that protrude sufiiciently in the forward direction toextend beyond the forward active end faces of said plurality ofpredetermined electroacoustical energy converter elements.

10. The device of claim 8, wherein said bafile comprises:

a ring1ike metallic frame having an open front end, a

recess of predetermined configuration and depth, and a closed rear endcontiguously disposed around the periphery of said metallic cup; and

a filler of rubber disposed within the recess of said frame.

11. The invention of claim 10, further comprising a predeterminedplurality of radially spaced, pyramidal shaped rubber wedges integrallyconnected to the forward surface of said filler in such manner as toprotrude sufficiently in the forward direction to extend beyond theforward active end faces of said plurality of predeterminedelectroacoustical energy converter elements.

12. The invention of claim 11, further comprising:

a bus bar eifectively connected to the rear end of said ring-likemetallic frame; and

a plurality of terminals extending through said bus bar and respectivelyconnected to the aforesaid electrical conductors.

References Cited UNITED STATES PATENTS 2,844,809 7/1958 Batchelder 3409UX 2,943,297 6/1960 Steinberger et al. 3409 3,059,130 10/1962 Robins3108.2 3,277,434 10/1966 Buchanan 3409 BENJAMIN A. BORCHELT, PrimaryExaminer H. TUDOR, Assistant Examiner U.S. Cl. X.R. 3l08.2, 9.6

